Part of my PhD focuses on figuring out how old a 12 mile long moraine (hill created by an ice sheet or glacier marking its edge) in central Wisconsin is. Below is a LiDAR hillshade DEM of Portage Co, the city of Stevens Point is located in the Western North Central part of this map. Over the past 120 years, geologists have used different kinds of dating tools to map out the moraines left behind by the Laurentide Ice Sheet during the Last Glacial Maximum (LGM), about 20,000 years ago.
In the map below, the moraines outlined in pink and orange (Hancock and Almond) were created by the ice sheet during the LGM, left behind once the ice sheet started melting and retreating. But the moraine outlined in blue (Arnott Moraine) has always stuck out to geologists as older due to it’s highly weathered surface and developed topography and its lower relief. The moraine is also covered with large erratic boulders left behind by an ice sheet, making it perfect for 10Be surface exposure dating, the technique that I know how to do. This technique makes it possible to “date” the boulders and constrain the age of the moraine, therefore figuring out when the ice sheet started retreating from that position.
During July-Sept 2017 I collected 33 boulder samples from the yards of private landowners and have gotten several exposure ages back. It turns out that the moraine is not as old as predicted by geologists throughout the 20th Century, who thought is was over 100,000 years old. My co-authors and I think it has something to do with permafrost, and how fast a landscape can degrade when the ground is frozen.